OPC Item Timestamps
Associated with each OPC item value is the time at which the value last changed or the value was refreshed. This is known as the OPC item timestamp.
The CIMPLICITY OPC Server synchronizes OPC item timestamps with point timestamps stored in the CIMPLICITY runtime database. When timestamps are not available from CIMPLICITY (as in the case where a CIMPLICITY project is stopped while OPC clients are connected), the OPC Server generates a timestamp based on the current computer node time.
Universal Coordinated Time
The OPC Server returns all timestamps to an OPC client in universal coordinated time (UTC). An OPC client must convert the timestamp to local time as required.
CIMPLICITY OPC Server technical notes.